The present invention relates to a coil-spring winding apparatus and, more particularly, to an improvement of means for guiding a coil spring on a mandrel.
A typical example of a conventional coil-spring winding apparatus comprises a mandrel and a lead screw extending parallel thereto. The lead screw is formed with a spiral groove which corresponds to the pitch and pitch angle of a coil spring. The mandrel and the lead screw are rotated in opposite directions. As the coil is guided onto the mandrel by the spiral groove, it is wound around the mandrel.
However, the designing and manufacture of the lead screw, in such a prior art apparatus, require much time and effort. Besides, the lead screw can be used for only one type of coil spring. Moreover, it is difficult to form a coil spring whose pitch angle changes drastically.
In a coil-spring winding apparatus disclosed in Japanese Patent Publication No. 20935/81, a guide roller is used in place of the lead screw. This winding apparatus comprises a mandrel and the guide roller spaced therefrom in the radial direction thereof. The guide roller is moved, by an actuator, in the axial direction of the mandrel, at a speed associated with the rotating speed of the mandrel. The coil is wound around the mandrel as it is guided by the guide roller.
Using the guide roller, the aforementioned winding apparatus does not require any large-sized, heavy member, such as the lead screw. Moreover, if the moving speed of the guide roller is continually changed, moreover, this apparatus can be applied to various types of coil spring. Since the mandrel and the guide roller are spaced widely apart, however, the coil cannot easily be guided to an accurate position on the mandrel. In forming a coil spring whose pitch angle varies considerably, the coil tends to slip on the mandrel, and therefore, cannot easily be wound at an accurate pitch angle.
In a winding apparatus stated in U.S. Pat. No. 3,610,006, the guide roller is located just over the mandrel. This prior art guide roller cannot, however, guide the coil in its first turn. In this winding apparatus, therefore, the coil is guided in its first turn by a guide finger which is provided independently of the guide roller and is located at a distance from the mandrel. Therefore, this conventional winding apparatus is disadvantageous in two respects. First, the guide finger requires precise and accurate control. Secondly, those turns of the spring, which forms the leading end thereof, are at a pitch differnt from the desired value.